Sensory auditory processing and intuitive sound detection : an investigation of musical experts and nonexperts

The auditory system can detect occasional changes (deviants) in acoustic regularities without the need for subjects to focus their attention on the sound material. Deviant detection is reflected in the elicitation of the mismatch negativity component (MMN) of the event-related potentials. In the studies presented in this thesis, the MMN is used to investigate the auditory abilities for detecting similarities and regularities in sound streams. To investigate the limits of these processes, professional musicians have been tested in some of the studies. The results show that auditory grouping is already more advanced in musicians than in nonmusicians and that the auditory system of musicians can, unlike that of nonmusicians, detect a numerical regularity of always four tones in a series. These results suggest that sensory auditory processing in musicians is not only a fine tuning of universal abilities, but is also qualitatively more advanced than in nonmusicians. In addition, the relationship between the auditory change-detection function and perception is examined. It is shown that, contrary to the generally accepted view, MMN elicitation does not necessarily correlate with perception. The outcome of the auditory change-detection function can be implicit and the implicit knowledge of the sound structure can, after training, be utilized for behaviorally correct intuitive sound detection. These results illustrate the automatic character of the sensory change detection function.

Cognitive Functioning in Young Adults with Depression, Anxiety Disorders, or Burnout Symptoms : Findings from a Population-based Sample

Background. Evidence of cognitive dysfunction in depressive and anxiety disorders is growing. However, the neuropsychological profile of young adults has received only little systematic investigation, although depressive and anxiety disorders are major public health problems for this age group. Available studies have typically failed to account for psychiatric comorbidity, and samples derived from population-based settings have also seldom been investigated. Burnout-related cognitive functioning has previously been investigated in only few studies, again all using clinical samples and wide age groups. Aims. Based on the information gained by conducting a comprehensive review, studies on cognitive impairment in depressive and anxiety disorders among young adults are rare. The present study examined cognitive functioning in young adults with a history of unipolar depressive or anxiety disorders in comparison to healthy peers, and associations of current burnout symptoms with cognitive functioning, in a population-based setting. The aim was also to determine whether cognitive deficits vary as a function of different disorder characteristics, such as severity, psychiatric comorbidity, age at onset, or the treatments received. Methods. Verbal and visual short-term memory, verbal long-term memory and learning, attention, psychomotor processing speed, verbal intelligence, and executive functioning were measured in a population-based sample of 21-35 year olds. Performance was compared firstly between participants with pure non-psychotic depression (n=68) and healthy peers (n=70), secondly between pure (n=69) and comorbid depression (n=57), and thirdly between participants with anxiety disorders (n=76) and healthy peers (n=71). The diagnostic procedure was based on the SCID interview. Fourthly, the associations of current burnout symptoms, measured with the Maslach Burnout Inventory General Survey, and neuropsychological test performance were investigated among working young adults (n=225). Results. Young adults with depressive or anxiety disorders, with or without psychiatric comorbidity, were not found to have major cognitive impairments when compared to healthy peers. Only mildly compromised verbal learning was found among depressed participants. Pure and comorbid depression groups did not differ in cognitive functioning, either. Among depressed participants, those who had received treatment showed more impaired verbal memory and executive functioning, and earlier onset corresponded with more impaired executive functioning. In anxiety disorders, psychotropic medication and low psychosocial functioning were associated with deficits in executive functioning, psychomotor processing speed, and visual short-term memory. Current burnout symptoms were associated with better performance in verbal working memory and verbal intelligence. However, lower examiner-rated social and occupational functioning was associated with problems in verbal attention, memory, and learning. Conclusions. Depression, anxiety disorders, or burnout symptoms may not be associated with major cognitive deficits among young adults derived from the general population. Even psychiatric comorbidity may not aggravate cognitive functioning in depressive or anxiety disorders among these young adults. However, treatment-seeking in depression was found to be associated with cognitive deficits, suggesting that these deficits relate to increased distress. Additionally, early-onset depression, found to be associated with executive dysfunction, may represent a more severe form of the disorder. In anxiety disorders, those with low symptom-related psychosocial functioning may have cognitive impairment. An association with self-reported burnout symptoms and cognitive deficits was not detected, but individuals with low social and occupational functioning may have impaired cognition.

The Freudian unconscious in the context of the cognitive orientation

For decades psychoanalysis was the discipline studying the unconscious, and other branches of study lacked competence to take a stand on the issues concerning the unconscious. From 1980s onwards intense study of the unconscious has been taken place in the scope of cognitive orientation. Thus, nowadays it is talked about both pyschoanalytic and cognitive unconscious. The aim of this thesis is to integrate psychoanalytic and cognitive views. When the "Freudian" conception of the unconscious is considered, there are four entangled issues: 1) what is the unconscious like, 2) how does the unconsciuos give rise to psychic disorders 3) why and how certain contents are missing from consciousness (repression of contents), 4) the emergence of those contents (becoming conscious of the repressed). The conventional psychoanalytic answer to the first question - and "the cornerstone of psychoanalysis" - is "the unconscious is mental". The issues 2)-4) depend radically on the answer given to the 1): "psychoanalytic" conceptualizations on them rest on the "cornerstone". That ground was challended in study I: it was argued that it has never been clear what does it mean that the unconscious is mental. Thus, it was stated that in the current state of art psychoanalysis should drop out the ephitet "mental" before the term unconscious. That claim creates a pressure to reappraise the convential "psychoanalytic" answers to the other questions, and that reappraisal was the aim of studies II and III. In study II the question 2) is approached in terms of implicit knowledge. Study III focuses on mechanisms, which determine which contents appear in the scope of consciousness, and also cause missing of contents from there (the questions 3) and 4)). In the core of study III there are distinctions concerning the processess occuring in the levels of the brain, consciousness, self-consciousness, and narrative self-consciousness. Studies I-III set "psychoanalytic" topics in the frames of cognitive view. The picture emerging from those studies is not especially useful for a clinican (psychotherapist). Studies IV and V focused that issue. Study IV is a rather serious critique toward neuropsychoanalysis. In it it was claimed that repressive functions of conscious states are in the core of clinical psychoanalysis, and functions in general cannot be reduced to neurophysiological terminology. Thus, the limits of neuropsychoanalysis are more strict than it has been realized: crucial clinical issues remain outside its scope. In study V it was focused on the confusing state of things that although unconscious fantasies do not exist, the idea on them has been an important conceptual tool for clinicans. When put in a larger context, the aim of study V is similar to that of study IV: to determine the relation between psychotherapists' and neuroscientists' terminologies. Studies III, IV and V apply the philosopher Daniel Dennett's model on different levels of explanation.

Cognitive deficits and the Paced Auditory Serial Addition Test performance among patients with multiple sclerosis

Multiple sclerosis (MS) is a chronic, inflammatory disease of the central nervous system, characterized especially by myelin and axon damage. Cognitive impairment in MS is common but difficult to detect without a neuropsychological examination. Valid and reliable methods are needed in clinical practice and research to detect deficits, follow their natural evolution, and verify treatment effects. The Paced Auditory Serial Addition Test (PASAT) is a measure of sustained and divided attention, working memory, and information processing speed, and it is widely used in MS patients neuropsychological evaluation. Additionally, the PASAT is the sole cognitive measure in an assessment tool primarly designed for MS clinical trials, the Multiple Sclerosis Functional Composite (MSFC). The aims of the present study were to determine a) the frequency, characteristics, and evolution of cognitive impairment among relapsing-remitting MS patients, and b) the validity and reliability of the PASAT in measuring cognitive performance in MS patients. The subjects were 45 relapsing-remitting MS patients from Seinäjoki Central Hospital, Department of Neurology and 48 healthy controls. Both groups underwent comprehensive neuropsychological assessments, including the PASAT, twice in a one-year follow-up, and additionally a sample of 10 patients and controls were evaluated with the PASAT in serial assessments five times in one month. The frequency of cognitive dysfunction among relapsing-remitting MS patients in the present study was 42%. Impairments were characterized especially by slowed information processing speed and memory deficits. During the one-year follow-up, the cognitive performance was relatively stable among MS patients on a group level. However, the practice effects in cognitive tests were less pronounced among MS patients than healthy controls. At an individual level the spectrum of MS patients cognitive deficits was wide in regards to their characteristics, severity, and evolution. The PASAT was moderately accurate in detecting MS-associated cognitive impairment, and 69% of patients were correctly classified as cognitively impaired or unimpaired when comprehensive neuropsychological assessment was used as a "gold standard". Self-reported nervousness and poor arithmetical skills seemed to explain misclassifications. MS-related fatigue was objectively demonstrated as fading performance towards the end of the test. Despite the observed practice effect, the reliability of the PASAT was excellent, and it was sensitive to the cognitive decline taking place during the follow-up in a subgroup of patients. The PASAT can be recommended for use in the neuropsychological assessment of MS patients. The test is fairly sensitive, but less specific; consequently, the reasons for low scores have to be carefully identified before interpreting them as clinically significant.

Cortical representations for phonological quantity

Different languages use temporal speech cues in different linguistic functions. In Finnish, speech-sound duration is used as the primary cue for the phonological quantity distinction ― i.e., a distinction between short and long phonemes. For the second-language (L2) learners of Finnish, quantity is often difficult to master if speech-sound duration plays a less important role in the phonology of their native language (L1). The present studies aimed to investigate the cortical representations for phonological quantity in native speakers and L2 users of Finnish by using behavioral and electrophysiological methods. Since long-term memory representations for different speech units have been previously shown to participate in the elicitation of the mismatch negativity (MMN) brain response, MMN was used to compare the neural representation for quantity between native speakers and L2 users of Finnish. The results of the studies suggested that native Finnish speakers' MMN response to quantity was determined by the activation of native-language phonetic prototypes rather than by phoneme boundaries. In addition, native speakers seemed to process phoneme quantity and quality independently from each other by separate brain representations. The cross-linguistic MMN studies revealed that, in native speakers of Finnish, the MMN response to duration or quantity-degree changes was enhanced in amplitude selectively in speech sounds, whereas this pattern was not observed in L2 users. Native speakers' MMN enhancement is suggested to be due to the pre-attentive activation of L1 prototypes for quantity. In L2 users, the activation of L2 prototypes or other L2 learning effects were not reflected in the MMN, with one exception. Even though L2 users failed to show native-like brain responses to duration changes in a vowel that was similar in L1 and L2, their duration MMN response was native-like for an L2 vowel with no counterpart in L1. Thus, the pre-attentive activation of L2 users' representations was determined by the degree of similarity of L2 sounds to L1 sounds. In addition, behavioral experiments suggested that the establishment of representations for L2 quantity may require several years of language exposure.

Human brain networks of auditory attention and working memory

This thesis examines brain networks involved in auditory attention and auditory working memory using measures of task performance, brain activity, and neuroanatomical connectivity. Auditory orienting and maintenance of attention were compared with visual orienting and maintenance of attention, and top-down controlled attention was compared to bottom-up triggered attention in audition. Moreover, the effects of cognitive load on performance and brain activity were studied using an auditory working memory task. Corbetta and Shulman s (2002) model of visual attention suggests that what is known as the dorsal attention system (intraparietal sulcus/superior parietal lobule, IPS/SPL and frontal eye field, FEF) is involved in the control of top-down controlled attention, whereas what is known as the ventral attention system (temporo-parietal junction, TPJ and areas of the inferior/middle frontal gyrus, IFG/MFG) is involved in bottom-up triggered attention. The present results show that top-down controlled auditory attention also activates IPS/SPL and FEF. Furthermore, in audition, TPJ and IFG/MFG were activated not only by bottom-up triggered attention, but also by top-down controlled attention. In addition, the posterior cerebellum and thalamus were activated by top-down controlled attention shifts and the ventromedial prefrontal cortex (VMPFC) was activated by to-be-ignored, but attention-catching salient changes in auditory input streams. VMPFC may be involved in the evaluation of environmental events causing the bottom-up triggered engagement of attention. Auditory working memory activated a brain network that largely overlapped with the one activated by top-down controlled attention. The present results also provide further evidence of the role of the cerebellum in cognitive processing: During auditory working memory tasks, both activity in the posterior cerebellum (the crus I/II) and reaction speed increased when the cognitive load increased. Based on the present results and earlier theories on the role of the cerebellum in cognitive processing, the function of the posterior cerebellum in cognitive tasks may be related to the optimization of response speed.

ADHD-aikuisten psykologinen kuntoutus : Neljän uuden lyhytintervention tutkimus

ADHD (attention deficit hyperactivity disorder) is developmental neurobiological disability. In adults, the prevalence of ADHD has been estimated to be about 4 %. In addition to the difficulties of attention, the problems in executive functioning are typical. The psychiatric comorbidities are common. The most extensively studied treatments are pharmacological. There is also evidence about the usefulness of the cognitive-behavioural therapy (CBT) in the treatment of adults with ADHD. There are some preliminary results about the effectiveness of cognitive training and hypnosis in children, but there is no scientific proof in adults. This dissertation is based on two intervention studies. In the first study, the usefulness of the new group CBT (n = 29) and the maintenance of the symptom reduction in the follow-up of six months were studied. In the second study, the usefulness of short hypnotherapy (n = 9), short individual CBT (n = 10) and computerized cognitive training (n = 9) were examined by comparing groups with each other and to the control group (n = 10). The participation in the group CBT and the participants' satisfaction were good. There were no changes in self-reports during waiting period of three months. After the rehabilitation, the symptoms decreased. Participants having symptom reduction during rehabilitation maintained their benefit through 6-month follow-up period. In a combined ADHD symptom score based on self-reports, seven participants in the hypnotherapy, six in the CBT, two in the cognitive training and two controls improved. Using independent evaluations, improvement was found in six of the hypnotherapy, seven of the CBT, two of the cognitive training and three of the control participants. There was no treatment-related improvement in cognitive performance. Thus, in the hypnotherapy and CBT groups, some encouraging improvement was seen. In the cognitive training group, there was improvement in the trained tasks but no generalization of the improvement. The results support the earlier results from the usefulness of CBT in the treatment of adults with ADHD. Also the hypnotherapy seems a useful rehabilitation. More research is needed to evaluate the usefulness of cognitive training. These promising results warrant further studies with more participants and with longer treatment duration. Also different measures of cognitive functioning and quality of life are needed. It is important in addition to the medication to arrange psychosocial interventions for the ADHD adults.

Neurochemical regulation of auditory information processing studied with EEG/MEG: application to schizophrenia

Cognitive impairments of attention, memory and executive functions are a fundamental feature of the pathophysiology of schizophrenia. The neurophysiological and neurochemical changes in the auditory cortex are shown to underlie cognitive impairmentsin schizophrenia patients. Functional state of the neural substrate of auditory information processing could be objectively and non-invasively probed with auditory event-related potentials (ERPs) and event- related fields (ERFs). In the current work, we explored the neurochemical effect on the neural origins of auditory information processing in relation to schizophrenia. By means of ERPs/ERFs we aimed to determine how neural substrates of auditory information processing are modulated by antipsychotic medication in schizophrenia spectrum patients (Studies I, II) and by neuropharmacological challenges in healthy human subjects (Studies III, IV). First, with auditory ERPs we investigated the effects of olanzapine (Study I) and risperidone (Study II) in a group of patients with schizophrenia spectrum disorders. After 2 and 4 weeks of treatment, olanzapine has no significant effects on mismatch negativity(MMN) and P300, which, as it has been suggested, respectively reflect preattentive and attention-dependent information processing. After 2 weeks of treatment, risperidone has no significant effect on P300, however risperidone reduces P200 amplitude. This latter effect of risperidone on neural resources responsible for P200 generation could be partly explained through the action of dopamine. Subsequently, we used simultaneous EEG/MEG to investigate the effects of memantine (Study III) and methylphenidate (Study IV) in healthy subjects. We found that memantine modulates MMN response without changing other ERP components. This could be interpreted as being due to the possible influence of memantine through the NMDA receptors on auditory change- detection mechanism, with processing of auditory stimuli remaining otherwise unchanged. Further, we found that methylphenidate does not modulate the MMN response. This finding could indicate no association between catecholaminergic activities and electrophysiological measures of preattentive auditory discrimination processes reflected in the MMN. However, methylphenidate decreases the P200 amplitudes. This could be interpreted as a modulation of auditory information processing reflected in P200 by dopaminergic and noradrenergic systems. Taken together, our set of studies indicates a complex pattern of neurochemical influences produced by the antipsychotic drugs in the neural substrate of auditory information processing in patients with schizophrenia spectrum disorders and by the pharmacological challenges in healthy subjects studied with ERPs and ERFs.

Luova mieli : lähikuvassa muusikoiden luomisprosessit

This work studied the creative process of musicians. The subject was chosen partly due to the attention given to creativity in social discussion. The approach was material-based, because during the work it became clear that the theoretical models describing the creative process in general did not provide adequate tools for the examination of musical creation. In this study, the creative process was defined as a process, which generated a work found by the musician novel to him or her. There were two principal research questions: 1) How does the creative process of musicians progress? 2) What makes a process creative? The main emphasis was on the first question, because the study aimed at modeling the creative process of musicians. The material for this study was collected by interviewing five professional musicians, each qualified by an expert of music to be creative. The interviews were thematically linked with each musician’s recently implemented creative process. The work generated in the process was used as a stimulant in the interview. The main themes of the interview dealt with the musician’s concrete action, cognitive functioning and affective experience during the process. Secondary themes included his or her goals as well as the factors that enhanced or inhibited the process. A material-based analysis was made of the interviews. The conceptualization and modelling of the creative process was founded on a phenomenological-hermeneutic interpretation. In addition to the primary interviews, also supplementary interviews were made in order to ensure that the description of the musician was understood correctly. Further supplementary interviews were made when the material was analyzed and results were deduced. This aimed at increasing the reliability of interpretations and conclusions. The study resulted in a four-level model representing the progress of a creative process. The levels were defined by means of the conception of state. The levels used in defining the process were 1) the state determining the potential of the process, 2) the state delimiting the process, 3) the state orienting the process, and 4) the state determined by the process. The progress of the process was described as changes taking place in the state. It was discovered that the factors having an effect on the creativity of the process were the dynamism of the process, the musician’s work in relation to his or her inner standard and the impulses that caused variation in the musician’s thinking. The interview method used in this study proved to be a very suitable tool in an examination of a creative process. Thus it may well be applicable in other research contexts associated with creative processes. The outcome of this study, the model of the progress of a creative process, should also provide a feasible basis for the examination of different kinds of creative processes. It enables a comprehensive examination of a creative process, simultaneously justifying the dynamic nature of the process.

Posttraumatic stress symptoms among school personnel after the Jokela school shooting : A longitudial study of exposure, interventions, and symptom changes

Objectives. School personnel who are exposed to school violence are at risk in developing post traumatic stress disorder (PTSD). In Finland there have been two such events in recent years, Jokela school shooting on 7.11.2007 and Kauhajoki school shooting about a year later. The aim of the present study was to examine the presence and change in PTSD symptoms during the first year after the Jokela school shooting. A second aim was to study how the initial exposure and treatment affects the symptom levels of PTSD. There were four hypotheses: 1) The PTSD symptoms are higher for the people who were exposed to the school shooting than for the people who did not face the stressor. 2) The PTSD symptoms increase in the follow up for the people at the school which was not attacked because of the second incident brought up the memories from the Jokela school shooting. 3) Those who have greater exposure to the shooting will have higher level of PTSD symptoms at both 4 and 11 months after the shooting than those who were not directly exposed to the shooting. 4) The PTSD symptoms are reduced more in the group that starts treatment right after the traumatic event than in other groups. Methods. A sample of 24 members of Jokela school personnel were examined four months after the incident and 16 were reassessed 11 month after the incident. To study the change and level of symptoms in other schools during the same period, a group with no exposure to the shooting was used as a control group (n=22). The assessment included Post Traumatic Stress Disorder Checklist Specific (PCL-S) and a social and professional support questionnaire. In addition questions about timing of support and experiences of psychological debriefing were asked. Results and conclusions. Most participants in the study group experienced some symptoms of PTSD at both 4 and 11 months. In both measures three participants from the study group fulfilled the diagnostic criteria for PTSD. The study group and control group differed significantly in overall symptom levels. The study group had more PTSD symptoms in the first measure but in the follow-up the study group’s PTSD symptoms decreased and the control group’s increased. There was a significant change in the study groups PTSD symptom level for those who started treatment right after the traumatic event. The results from this study showed that an exposure to school shooting has long-term effects on school personnel. The findings suggest that it is crucial to plan a comprehensive and long-term treatment for school personnel in the aftermath of school shooting.

Viisi vuotta tiedonrakentamista yhteisö- ja teknologiaelementtien muovautumisen näkökulmasta

The object of this study was to examine the phenomena of a long-term Knowledge Building process. The subject was OECD/ENSI/FI-project's Knowledge Building in Knowledge Forum®3.4 environment from 8.9.2000 to 8.9.2005. Research was based on socio-cognitive and socio-cultural learning approaches and the theoretical background consisted of models of collaborative learning and knowledge processing. These theoretical applications were first structured using metaphors of language and then assembled into five main theoretical motifs. The main motifs were 1) context, 2) inter-subjective, shared area, 3) community's practices and participation, 4) developing expertise and 5) the sequential construction of processes. These themes were assembled in interpreting the results using the Mutual Shaping of Technological and Social Elements by Boczkowski (1999) as a conceptual tool. The social elements of the mutual shaping process were defined as 1) community structure, 2) discourse and 3) the meanings of activity. The technological elements were defined as 1) shared artefacts, 2) features of technology-use and 3) other technological conventions perceived in activity. The five main theoretical motifs were used as the basis for creating the research problems, which were divided into three themes: 1) shared artefacts, themes of Knowledge Building and participant formation, 2) patterns of participation and interaction and 3) the meanings of activity. As methods I used content analysis of the messages, the quantitative profiling of changes in the database, social network analysis, discourse analysis of selected message threads and theme interviews of eleven participants. Based on my study it's possible to say, that a long-term setting of this kind provides a different perspective on Knowledge Building from most of the previous research. The most valuable conclusions from the data are: 1) The centralisation of interaction in this type of setting is a feature that supports the improvement in the quality of action. 2) The participation in a long-term Knowledge Building process seems to support the concious effort on professional development and the expert-identity. 3) The quality of plasticity of the technology-in-use has implication for how the communal features of activity will develop. The agency is seen to initiate processes that in turn open up new possibilities for the quality of action on both the communal and individual levels.

Sleep deprivation and brain energy metabolism : in vivo studies in rats and humans

Sleep deprivation leads to increased subsequent sleep length and depth and to deficits in cognitive performance in humans. In animals extreme sleep deprivation is eventually fatal. The cellular and molecular mechanisms causing the symptoms of sleep deprivation are unclear. This thesis was inspired by the hypothesis that during wakefulness brain energy stores would be depleted, and they would be replenished during sleep. The aim of this thesis was to elucidate the energy metabolic processes taking place in the brain during sleep deprivation. Endogenous brain energy metabolite levels were assessed in vivo in rats and in humans in four separate studies (Studies I-IV). In the first part (Study I) the effects of local energy depletion on brain energy metabolism and sleep were studied in rats with the use of in vivo microdialysis combined with high performance liquid chromatography. Energy depletion induced by 2,4-dinitrophenol infusion into the basal forebrain was comparable to the effects of sleep deprivation: both increased extracellular concentrations of adenosine, lactate, and pyruvate, and elevated subsequent sleep. This result supports the hypothesis of a connection between brain energy metabolism and sleep. The second part involved healthy human subjects (Studies II-IV). Study II aimed to assess the feasibility of applying proton magnetic resonance spectroscopy (1H MRS) to study brain lactate levels during cognitive stimulation. Cognitive stimulation induced an increase in lactate levels in the left inferior frontal gyrus, showing that metabolic imaging of neuronal activity related to cognition is possible with 1H MRS. Study III examined the effects of sleep deprivation and aging on the brain lactate response to cognitive stimulation. No physiologic, cognitive stimulation-induced lactate response appeared in the sleep-deprived and in the aging subjects, which can be interpreted as a sign of malfunctioning of brain energy metabolism. This malfunctioning may contribute to the functional impairment of the frontal cortex both during aging and sleep deprivation. Finally (Study IV), 1H MRS major metabolite levels in the occipital cortex were assessed during sleep deprivation and during photic stimulation. N-acetyl-aspartate (NAA/H2O) decreased during sleep deprivation, supporting the hypothesis of sleep deprivation-induced disturbance in brain energy metabolism. Choline containing compounds (Cho/H2O) decreased during sleep deprivation and recovered to alert levels during photic stimulation, pointing towards changes in membrane metabolism, and giving support to earlier observations of altered brain response to stimulation during sleep deprivation. Based on these findings, it can be concluded that sleep deprivation alters brain energy metabolism. However, the effects of sleep deprivation on brain energy metabolism may vary from one brain area to another. Although an effect of sleep deprivation might not in all cases be detectable in the non-stimulated baseline state, a challenge imposed by cognitive or photic stimulation can reveal significant changes. It can be hypothesized that brain energy metabolism during sleep deprivation is more vulnerable than in the alert state. Changes in brain energy metabolism may participate in the homeostatic regulation of sleep and contribute to the deficits in cognitive performance during sleep deprivation.